Phase formation and conductivity fluctuation investigation in nanoparticle SnO$_2$-added Y$_3$Ba$_5$Cu$_8$O$_{18\pm\delta}$ polycrystalline superconductor

The influence of 0.00, 0.20, 0.40, 0.50, and 0.60 wt % nano-sized tin oxide (SnO$_2$) particles on electrical conductivity fluctuation in normal and superconducting state of the Y$_3$Ba$_5$Cu$_8$O$_{18\pm\delta}$ (denoted as Y-358) polycrystalline samples is studied. Phase formation and microstructures have been systematically examined. By increasing the content of SnO$_2$ in YBCO matrix, X-ray diffraction technique showed slight variation in lattice parameters and overall reduction in the orthorhombicity. Scanning electron microscopy observations and the crystallite size calculation also revealed that the grain size and the average crystallite size decreased compared to the SnO$_2$-free sample. Aslamazov–Larkin and Lawrence–Doniach prototypes were used to analyze conductivity fluctuations based on the electrical resistivity $\rho(T)$ measurements. Superconducting transition temperatures $T_c$ and $T_{\mathrm{LD}}$ have been reported. The influence of SnO$_2$ addition on the superconducting properties indicates that with the addition of SnO$_2$ nanoparticles into Y-358 compound, some parameters values such as zero-resistance critical temperature $T_{c\operatorname{zero}}$, coherence distance alongside the $c$ axis at 0 K $\xi_c (0)$, and super-layer length $d$ decrease in total, while anisotropy $\gamma$, critical magnetic fields $B_{c1}(0)$, $B_{c2}(0)$, and critical current density $J_c (0)$ increase in SnO$_2$-added Y-358 specimens compared to the pure one. The reasons corresponding to these scenarios are discussed in details.